1. Field of the Invention
This invention relates to a temporary ink storage member for temporarily storing ink so as to suppress excess discharge and prevent insufficient discharge of ink due to changes in temperature and pressure when ink inside an ink tank is supplied to a pen tip. The invention further relates to a writing instrument having this temporary ink storage member inside a shaft body between a pen tip and an ink tank.
2. Description of the Prior Art
Writing instruments storing therein ink can be classified broadly into two kinds, depending on the mode of storage of ink. One kind utilizes an ink absorption member which functions to retain ink by utilizing the capillary force of, for example, a fiber aggregate, and the other kind merely stores ink in a container-like ink tank without relying in particular on the capillary force, as typified by an ordinary fountain pen.
As is well known, the latter generally uses a member for storing temporarily ink in order to prevent the occurrence of excess of insufficient ink supply from the ink tank to the pen tip due to changes in temperature and pressure.
Various contrivances have been made in the past in order to have the temporary ink storage member fully perform its functions.
Japanese Utility Model Publication No. 32790/1986, for example, discloses a device wherein the capillary force of each member forming the temporary ink storage member is different from other members forming the temporary ink storage member, wherein the members are arranged in a predetermined order so as to improve reliability of the ink storage function.
Besides the prior art reference described above various shapes and structures of temporary ink storage members are known, but most of them are made of a synthetic resin by injection molding. A large member of high quality writing instruments have been proposed, and put into practical application as products, due to various contrivances for the temporary ink storage member. However, they are not yet entirely satisfactory.
The greatest problem lies in that a temporary ink storage member capable of storing a large quantity of ink has not yet been invented. The capacity of the ink tanks of fountain pens that are now available on the market, for example, is about 1 cc and at most about 2 cc. However, a temporary ink storage member of a writing instrument capable of storing a large quantity of ink must itself be capable of storing a large quantity of ink.
The conditions that must be satisfied in order to let the temporary ink storage member fully perform its functions are listed below.
(1) The temporary ink storage member must be able to store a quantity of ink corresponding to an expansion quantity of air when air inside the ink tank expands, in order to prevent ink from flowing out. PA0 (2) It must be able to preferentially return more ink, rather than air, to the ink tank when the volume of air inside the ink tank shrinks. If air enters the ink tank while ink temporarily remains in the ink storage member, the quantity of ink that is left inside the temporary ink storage member increases gradually over repeated cycles of volume changes of the air in the ink tank, until it reaches a point where the temporary ink storage member will no longer function. PA0 (3) If the temporary ink storage member stores ink when ink is consumed by the pen tip during writing, the temporary ink storage member must be able to preferentially supply this stored ink to the pen tip rather than the ink inside the ink tank, or must be able to preferentially return this stored ink to the ink tank rather than air, in order to prevent the drop of the pressure of the ink tank due to consumption of ink from the ink tank by the pen tip. This is due to the same reason as the condition (2) described above. PA0 (4) The temporary ink storage member must have a high capillary force portion. Since an ink tank opening other than the pen tip is formed, ink will flow more than necessary and result in leakage of ink, unless the capillary force is sufficiently high. PA0 (5) The capillary force of the condition (4) must not be excessively high. If it is higher than that on the pen tip side, the movement of ink due to the change of the internal pressure of the ink tank will occur on the pen tip side. In addition, when ink is consumed by the pen tip during writing, ink staying in the temporary ink storage member then returns to the ink tank and the air enters the ink tank and must rupture the film of ink. However, a certain level of force is necessary to rupture this ink film and if this force is too strong, the pressure in the ink tank will drop and, eventually, the supply of ink to the pen tip will become insufficient. Besides these various conditions described above, the following practical condition (6) must be satisfied. PA0 (6) The temporary ink storage member must have a large bulk capacity. If the bulk capacity is great, the quantity of ink that can be stored in the ink tank must be reduced as much, or the size of the writing instrument must be increased.
To satisfy all the conditions described above, extremely complicated and precision molded articles must be produced. The thickness of the portion forming the ink storage portion, for example, is ordinarily below 1 mm. Moreover, the ink storage portion for retaining ink by the capillary force is molded with a width of 0.2 or 0.3 mm. The number of such molded articles may be small if it is small as a whole but molding becomes more difficult with increasing size. For example, in the apparatus disclosed in the above-mentioned prior art publication, it is extremely difficult to obtain a practical molded article, and dimensional variance resulting from molding must also be taken into consideration. Even if the problems of molding, which become greater if the ink storage portion has a greater size, are solved, it becomes more difficult to fundamentally satisfy the conditions (2) and (3) described above, because the distance over which ink must move becomes greater.